The present invention relates to a transmission for an automotive vehicle, and in particular relates to an automatic type transmission particularly suitable for use in a transverse front engine front wheel drive type automotive vehicle, or a so called FF vehicle.
There is a known type of front engine type front wheel drive type automotive vehicle in which the internal combustion engine thereof is mounted transversely to the vehicle body, with its crankshaft extending at right angles to the longitudinal axis of the automotive vehicle body, and in which the automatic transmission thereof is attached to the internal combustion engine with the directions of the rotational axes of the various mechanisms contained therein likewise extending transversely to the longitudinal axis of the vehicle body. In such a transverse type of construction, it is very important to keep the axial length of the automatic transmission as short as possible, so as to fit the transmission mechanism and the rotary power train of the vehicle as a whole into the shortest possible space, in view of the severe restriction imposed on the axial length of this rotary power train by the overall width of the vehicle, within which of course the rotary power train must be accomodated.
There is a well known per se form of transmission which has been evolved as suitable for such transverse mounting, in which a fluid torque converter is mounted to the internal combustion engine and is placed coaxially with said engine and with a gear transmission mechanism along a first axis and drives said gear transmission mechanism, and in which the rotary power output from said gear transmission mechanism is transferred sideways from said first axis to a lay shaft which extends along a second axis parallel to said first axis back under the gear transmission mechanism to a point approximately under the torque converter, where this engine side end of the lay shaft is rotationally connected to a differential device appropriate for a front wheel drive configuration.
This configuration of automatic transmission has been successfully implemented in the past, but owing to the limited space available along said first axis for providing said gear transmission mechanism the design process, manufacture, assembly, and servicing therefore have been rather difficult. Further, in line with the ever increasing requirements for smaller and smaller automotive vehicles, there has been recently a need to adapt these automatic transmissions to vehicles having even smaller widths than heretofore, which has been very difficult, in view of the problems in design, manufacture, assembly, and servicing outlined above.
Also, in the construction of such an automatic transmission, the compactness in the directions sideways from the axial direction described above which is transverse to the vehicle axis is important; in other words, it is important that the transmission not be too fat; and more particularly it is important that there not be too much of a bulge created by providing space within the transmission for accomodating the gear train which is necessarily provided for driving the above described lay shaft from the power output member of the gear transmission mechanism. The reduction of such a bulge, especially of the bulge at the lower side of the transmission around the end of the lay shaft, is important in view of the problem of interference between such a bulge and the drive shaft which drives the front wheel on that side of the automotive vehicle, which sometimes presents a problem.
Further, in the past, difficulties have been experienced with regard to making the transmission, and particularly the internal construction thereof, strong enough to be durable over a long period of time; in particular the lay shaft structure has experienced problems with regard to strength, which have affected its durability. The weight of the transmission as a whole, and the weight of the lay shaft structure in particular, also in some cases are critical design factors with regard to such a transmission. Finally, the question of noise produced by the gears in such a transmission, and in particular the question of the noise produced by the lay shaft assembly, is important from the point of view of producing a transmission which is environmentally acceptable, as well as being easy and pleasant of operation by the driver of the vehicle, especially over a long period. This has importance with regard to questions of drivability of the vehicle as a whole. These questions of noise, and of durability, are related to the desire to simplify the bearing structure of such a lay shaft construction.